Conventional exhaust systems for inboard/outboard marine propulsion systems direct water-cooled exhaust from an inboard mounted marine engine through the transom and into the outdrive. The water-cooled exhaust passes through the outdrive and exits through the propeller hub into the surrounding water. In an engine with a V-style engine block, the exhaust system usually includes rigid intermediate exhaust elbows and a rigid bullhorn. The bullhorn is a unitary exhaust system component comprising rigid exhaust pipes and an integral water separator. The intermediate exhaust elbows direct water-cooled exhaust gases and spent cooling water from exhaust elbows located on the engine to the bullhorn. The water separator in the bullhorn separates the liquid water from the water-cooled exhaust gases by forcing the liquid to flow into a separated lower passage located underneath a passage for the gases. The water and exhaust gases are then discharged through the transom into the outdrive. The water is expelled through holes in the side of the outdrive. The exhaust gases flow through the outdrive and are discharged through the propeller hub. Other configurations for exhaust systems in inboard/outboard marine propulsion systems are sometimes used. In some of these systems, the exhaust pipes are physically separated from the water separator and the exhaust pipes are bolted onto the water separator.
Conventional exhaust systems for inboard/outboard marine propulsion systems, while providing adequate means for discharging exhaust gases and cooling water, have significant limitations with regard to their installation and maintenance. With conventional exhaust systems, it is usually important to install the exhaust system before the engine is installed. Also, precise installation of both the exhaust system and the engine is required so that exhaust system interconnections are properly matched. Normally, there is almost no room available for adjustment between the exhaust pipe inlets and the engine exhaust elbow outlets after the engine has been installed. Furthermore, when the exhaust pipes need to be repaired, replaced, or serviced, the engine must normally be removed entirely (or at least loosened on the mounting brackets) to allow sufficient access to the intermediate exhaust pipes and bullhorn.